GB1276653A - Recovery of gases - Google Patents

Abstract

1276653 Centrifugal separation of gases PETROCARBON DEVELOPMENTS Ltd. 19 Aug 1969 [20 Aug 1968] 39734/68 Heading B2P [Also in Division F1] Hydrogen or helium of increased purity is obtained from a gaseous mixture consisting predominantly of hydrogen or helium by introducing the gaseous mixture into the central part of a rotating gas centrifuge rotor under such conditions of temperature and pressure that the gaseous mixture is above its dew point but passes through its dew point as it is caused by centrifugal force to pass to the peripheral wall of the centrifuge rotor, the temperature being maintained substantially constant throughout the centrifuge, whereby an increase in pressure and a decrease in hydrogen or helium concentration results so that gaseous impurities are condensed and collect on the wall of the rotor and a hydrogen or helium gas stream of increased purity is recovered from the gas centrifuge. For mixtures of H 2 or He containing N 2 , and which may also contain CH 4 CO and/or A, temperatures of 64-110‹K and pressures of 10-50 atm. abs. may be used. The gaseous mixture may be subjected to a two-stage process in the gas centrifuge or it may first be subjected to a low temperature condensation process to increase the percentage of H 2 , or He in the mixture before centrifugation. The gas stream recovered from the centrifuge may be further purified by means of an adsorption or diffusion process. In one example of the process applied to the recovery of helium from natural gas containing He, N 2 and CH 4 , the gas is compressed and cooled in a separate plant to remove most of the CH 4 and some of the N 2 . The gas is then passed via a line 50, Fig. 2, through a heat exchanger 51 whereby the residual CH 4 and most of the N 2 are condensed. The resulting gas and liquid phases are passed by line 52 into a separator 53. The separated liquid from separator 53 passes through line 54 and expansion valve 55 to the heat exchanger 51 in which it is completely evaporated and which it leaves through line 56 to be returned to the previous separate plant. The gas phase from the separator 53 is fed via a line 57 to a centrifuge 58 driven by a gas expansion turbine 60. N 2 is liquefied in centrifuge 58 and is withdrawn from the centrifuge rotor periphery and passed through line 65 and expansion valve 66 to be mixed with the liquid from separator 53 downstream of valve 55. The temperature in the centrifuge is kept constant by controlling the pressure upstream of the valve 66. The purified He gas leaves the centrifuge through line 61, is warmed in heat exchanger 51 and passes via line 62 to the turbine 60 in which it is expanded and cooled. The cooled He gas leaves through line 63 and passes through heat exchanger 51 from which it is returned via line 64 to the previous plant. Another example applied to the recovery of hydrogen from ammonia synthesis purge gas is described. The centrifuge may be as shown in Fig. 3, its barrel-shaped rotor 34 being integral with an inward radial flow expansion gas turbine wheel 32 which drives a shaft 33 and is integral with a rotating tube 36 which carries away the exhaust gas to an outlet 37. A stationary tube 38 surrounds the tube 36 leaving an annulus through which a hydrogen-nitrogen gas mixture fed at 39 passes and enters the centrifuge rotor at 40. The light H 2 gas leaves the rotor at 41 and passes to outlet 42. The liquefied N 2 collects on the wall 43 of the centrifuge rotor and passes through openings 44 in the wall of the rotor and into the space between the rotor and a surrounding casing 45 to leave by outlet 46. The shaft 33 is connected to a compressor. Labyrinth seals are provided at 47. The bearing 49 for the tube 36 also acts as a seal. The turbine wheel 32 may be made of stainless steel or aluminium, the centrifuge rotor 35 of stainless steel and the casing 45 of aluminium.